The trans-polypentenamer has unique relevance among the synthetic rubbers since it has similar physical properties to natural rubber. Polypentenamer additives have a propitious effect on the tire properties and have been studied extensively for this application. They can be synthesized by equilibrium ring-opening metathesis polymerization (ROMP) using well-defined ruthenium catalyst systems. This unique feature of the equilibrium polymerization opens a way for the synthesis of durable, environmentally friendly elastomers where tires can not only be synthesized but also readily recycled by the same transition metal catalyst system.
Linear polyhydroxy polymers have found use in the food packaging and in biomedical and pharmaceutical industries. Here we are also reporting a synthetic methodology where polyhydroxy polypentenamers can be synthesized with acyclic diene metathesis polymerization (ADMET) or ROMP reactions. The polarity of the polymer can be easily fine tuned with the co-polymerization with cyclopentenes.
Copolymers of polyvinyl alcohol (PVA) are widely used as adhesives in coatings and packaging materials because of their excellent barrier properties towards hydrocarbons and gases. Moreover, these hydrophilic synthetic resins have many biomedical applications. The concentration of hydroxyl groups along the polymer chain determines its polarity, and thus the barrier properties of the polymer. Ethylene-(vinyl alcohol) (EVOH) copolymers with higher vinyl alcohol content have better barrier properties. Additionally, tuning of the polarity of PVA copolymers used in drug delivery applications can control targeted drug release. For example, the 5-fluorouracil (5-FU) anticancer agent release can be easily controlled by modifying the vinyl alcohol and ethylene proportions in the copolymer. These polymer matrices can be used as tunable implanted delivery systems in cancer chemotherapy.
There are a number of reported synthetic procedures for such polymers; however, syntheses of highly controlled and well-defined alternating polymers are rare (see Li, Z.; Lv, A.; Li, L.; Deng, X.; Zhang, L.; Du, F.; Li, Z. Polymer 2013, 54, 3841; Valenti, D.; Wagener, K. Macromolecules 1998, 31, 2764). A variety of polymerization techniques for the synthesis of PVA copolymers have been reported previously: ruthenium-catalyzed ROMP (see Scherman, O.; Kim, H.; Grubbs, R. Macromolecules 2002, 35, 5366), cationic group-transfer polymerization (see Mori, Y.; Sumi, H.; Hirabayashi, T.; Inai, Y.; Yokota, K. Macromolecules 1994, 27, 1051), palladium-catalyzed ethylene-vinyl acetate copolymerization (Ito, S.; Munakata, K.; Nakamura, A.; Nozaki, K. Journal of the American Chemical Society 2009, 131, 14606), and free radical polymerization (see Sato, T.; Okaya, T. Makromolekulare Chemie-Macromolecular Chemistry and Physics 1993, 194, 163).
Synthesis of PVA copolymers via ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) or acyclic diene metathesis polymerization (ADMET) reactions have been reported. Hillmyer reported the synthesis of linear hydroxyl-functionalized polyoctenamers via ruthenium metathesis catalyst initiated ROMP of hydroxy functionalized cyclooctene (COE) (see Hillmyer, M.; Laredo, W.; Grubbs, R. Macromolecules 1995, 28, 6311). An alternative way to linear hydroxyl functionalized polyoctenamers is the ROMP of borane substituted COE with early transition metals followed by oxidation (see Ramakrishnan, S.; Chung, T. Macromolecules 1990, 23, 4519). Recently Li et al. reported the ADMET of two vinyl acetate-containing symmetrical □□ω-diene monomers (see Li, Z.; Lv, A.; Li, L.; Deng, X.; Zhang, L.; Du, F.; Li, Z. Polymer 2013, 54, 3841). Wagener et al. synthesized well-defined ethylene-vinyl alcohol copolymers via ADMET of the corresponding symmetrical □□ω-diene monomers and also introduced primary, secondary and tertiary hydroxyl groups in precise intervals into the polyolefin chain. Well-defined ethylene-vinyl alcohol copolymers were obtained following hydrogenation using this method (see Valenti, D.; Wagener, K. Macromolecules 1998, 31, 2764). Scherman et al. reported the synthesis of poly(vinylalcohol2-alt-methylene) via the ROMP of a “temporary” strained cis-4-cyclopentene-1,3-diol and two post-polymerization modifications, both under forcing conditions (FIG. 1) (see Scherman, O.; Kim, H.; Grubbs, R. Macromolecules 2002, 35, 5366).
The ADMET of acetyl group protected 1,6-heptadiene-4-ol has been investigated at relatively high temperature (60° C.); it was found that the reaction stops at the ring-closed intermediate and the subsequent ROMP step did not occur (see Li, Z.; Lv, A.; Li, L.; Deng, X.; Zhang, L.; Du, F.; Li, Z. Polymer 2013, 54, 3841. The ROMP of cis-4-cyclopentene-1,3-diol is not feasible due to the low ring strain energy of the cyclopentene ring (2.29 kcal/mol) (see Scherman, O.; Kim, H.; Grubbs, R. Macromolecules 2002, 35, 5366). Preliminary thermodynamic investigations and theoretical ring strain energy calculations revealed, however, that the non-protected 3-cyclopentene-1-ol (2) has moderate strain energy that is slightly higher than that of cyclopentene (1), which is known to polymerize in equilibrium ROMP.
Strategies which would produce highly-polar, well-defined PVA alternating copolymers via one-pot equilibrium olefin metathesis reactions such as the ROMP of 3-cyclopenten-1-ol (2) and the ADMET of 1,6-heptadiene-4-ol (10), have not yet been investigated.
Cyclic polymers exhibit a number of unique properties in comparison to their linear analogues such as increased hydrodynamic radii, functional group density, lower viscosity, and higher thermal stability, resulting in better performance in their applications. Moreover, the lack of chain ends characteristic of cyclic topologies could have significant ramifications for material applications. For example, linear polymer end groups are thought to contribute to the overheating of tires, significantly reducing tire adhesion and carcass durability. Cyclic polymers are thus expected to at least partially mitigate these issues and improve tire performance. Polypentenamers are a particularly attractive system to compare linear and cyclic topologies due to both similarities with natural rubber (see G. Natta, I. Bassi, Journal of Polymer Science Part C-Polymer Symposium 1967, 2551) and synthetic accessibility. Although in the past couple of decades a number of new cyclopolymer synthetic techniques have been developed, cyclopolypentenamer synthetic rubbers have not yet been synthesized.
Therefore, despite the advances achieved in the art, a continuing need exists for further improvements and for new polymer materials.